Хятадын өмнөд хэсгээс олдсон Юрийн галавын үеийн Zhengheornis buyu хэмээх жижиг шувууны чулуужсан яс нь шувуудын хувьслын хамгийн том таавар болох сүүлний бүтцийн өөрчлөлтийг тодруулж байна.
Хятадын Шинжлэх ухааны академийн палеонтологичдын 2024 онд Фужян мужийн Жэнхэ тойргоос илрүүлсэн энэхүү олдвор нь 148–150 сая жилийн тэртээх үед хамаарч байна. Science Advances сэтгүүлд нийтлэгдсэн судалгаагаар, энэ шувуу нь сүүлийн үеийн шувуудын адил сүүлний өд бэхлэгддэг “пигостиль” буюу ясны нэгдсэн бүтэцгүй боловч сүүл нь богиноссон шинжтэй байжээ.
Судлаачдын тогтоосноор, Zhengheornis buyu нь ердөө 15 нугаламтай сүүлтэй байсан нь өмнөх үеийн шувуудын 23–30 гаруй нугаламтай харьцуулахад эрс богино юм. Энэхүү анатомийн холимог шинж нь шувуудын хувьслын явцад сүүлний нугалам эхлээд богиносож, харин пигостиль яс нь хожим бүрэлдсэнийг нотолж байна.
74–163 грамм жинтэй гэж тооцоолсон энэхүү амьтан нь пигостиль бүтэцгүй, өнөөг хүртэл олдсон хамгийн жижиг насанд хүрсэн теропод шувуу юм. Энэхүү олдвор нь Юрийн галавын төгсгөл гэхэд шувууд төрөл зүйлийн хувьд аль хэдийн өргөн тархаж, хувьслын томоохон үе шатыг туулсныг баталж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
A newly identified bird from the Late Jurassic is helping fill one of the biggest gaps in bird evolution. Named Zhengheornis buyu, the tiny species had a shortened tail without the fused tailbone seen in modern birds. The fossil was unearthed in southeastern China and described in Science Advances.
The research suggests that specimens first evolved shorter tails before developing the pygostyle, the fused structure that supports the tail feathers of living birds. Modern birds are the only vertebrates with a short tail ending in a pygostyle. That feature anchors the fan of tail feathers used during flight. Their dinosaur ancestors, on the other hand, carried long, bony tails made up of dozens of vertebrae. Exactly how one body plan evolved into the other has remained difficult to explain because fossils capturing the transition are exceptionally rare.
For years, paleontologists debated whether tail shortening and pygostyle formation happened at the same time. The anatomy of Zhengheornis buyu now provides new evidence that these changes unfolded in separate stages.
A Tiny Fossil From China Reveals a Missing Link
The holotype of Zhengheornis buyu was discovered in 2024 in the Nanyuan Formation near Yangyuan village in Zhenghe County, Fujian Province. The study, published in Science Advances, dates the fossil to between 148 and 150 million years ago, placing it near the end of the Jurassic Period. The species is the fourth bird identified from the Zhenghe Fauna. The site has also produced Fujianvenator, Baminornis, and another incomplete bird known only from a preserved furcula, or wishbone.
Dr. Zhonghe Zhou, a paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, said long-tailed and short-tailed birds appear almost simultaneously in the early fossil record, with no clear intermediate forms.
Because of this, many evolutionary biologists believed that a bird with a short but completely unfused bony tail was unlikely to have ever existed.
A Short Tail With No Pygostyle
The new species stands out because of its unusual tail anatomy. Zhengheornis buyu had only 15 tail vertebrae, far fewer than the 23 or 24 found in Archaeopteryx and the more than 30 seen in several other early bird relatives. Even with its shorter tail, the vertebrae had not fused into a pygostyle. The last two tail bones are also box-shaped, a feature previously reported only in the distantly related dinosaur Caudipteryx.
Dr. Min Wang, who also took part in the research at the Chinese Academy of Sciences, said this anatomical combination shows that vertebral reduction and tail shortening came before pygostyle fusion during early bird evolution.
“This anatomical mosaic proves a stepwise evolutionary path: the vertebral reduction and shortening preceded pygostyle fusion in early bird evolution,” the authors described.
One of the Smallest Early Birds
The researchers estimated the bird’s body mass from the length and circumference of its thigh bone. Their calculations place it between 74 and 163 grams, making it smaller than the diminutive specimen long considered the smallest known Archaeopteryx.
The team writes that the holotype of Zhengheornis buyu is the smallest adult non-pygostylian theropod identified so far. At the same time, its skeleton does not clearly indicate whether it was adapted to life in trees or on the ground.
The study also highlights differences among the birds that lived within the Zhenghe Fauna. Body size, skeletal architecture and ecological preferences varied across the group, from the more generalist Zhengheornis buyu to the cursorial Fujianvenator.
The authors also added that this diversity shows that avialans had already undergone a major adaptive radiation by the end of the Jurassic Period, helping resolve a long-running debate over when early birds first diversified.
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